Design and Optimization of a Novel Large-scale Process for Natural Gas Liquefaction

Abstract

Natural Gas Liquefaction (LNG) is increasingly emerging as the ideal transition fuel to meet the world's growing energy demand. With the anticipated increase in LNG's market share over the upcoming decades, there is an urgent need to develop innovative processes that support the transition to more cost-effective and energy-efficient solutions. Although many LNG processes have been developed, they are still energy inefficient. This dissertation examines the state-of-the-art natural gas liquefaction processes and optimization techniques, focusing on cascade-based processes due to their relatively higher efficiency. Consequently, a design and optimization methodology is proposed to improve the CryoMan process, aiming to develop a novel process that reduces the power consumption and operational costs for large-scale production. Initially, a base case for the bypass CryoMan process is established. Then, various modified designs were explored and simulated, leading to the selection of a design that yields the lowest total shaft work. Lastly, an optimization framework is introduced, combining feasible simulation results using rigorous models and sensitivity analyses to determine the boundary conditions for the optimization. Moreover, a deterministic optimization approach, utilizing Aspen HYSYS’s mixed scheme, is employed to minimize the shaft work of the selected design. Through this rigorous process, the proposed design initially achieved a 1.98% decrease in the total shaft work compared to the base case. Further adjustments to the variables and their boundary conditions led to the optimization results showing a 9.32% reduction in energy consumption compared to the base case, translating to a potential annual saving of about $11.6 million. The results of this dissertation confirm the potential of structural changes in SMR-based cascade processes and the economic benefits of these modifications. These findings are of notable importance for the LNG industry, indicating that significant reductions in energy consumption and cost are attainable in large-scale natural gas liquefaction processes.